This invention relates to long rod penetrators, and more specifically relates to a novel structure for severably securing guide fins to a long rod body so that the guide fins are sheared from the body with a minimum reduction in penetrating force of the long rod as it penetrates armor.
Long rod penetrators are well known and are adapted to penetrate armor. Long rod penetrators have stabilizing fins which are either welded to the penetrator rod or threadably fixed to the penetrator rod. Such stabilizing fins are necessary to guide the penetrator in true flight to the target. In conventional long rod penetrators, if armor is thick enough, it is possible that the long rod remains unpenetrated if the fins remain at least partly locked to the penetrator or are only partly sheared from the penetrator as the penetrator moves through the armor.
It would, of course, be desirable to reduce the retardation effect of the fins which may prevent the penetrator from moving as far through the armor as possible. This problem is intensified when using stronger ferrous type materials for the guide fins and penetrator rod to accommodate new propellants which expose the assembly to higher temperatures. Thus, armor is constantly being improved in toughness, hardness, obliquity and is being constructed in multilayer fashion. All of these changes require improvements in penetrators by increasing penetrating power and range. Such improvements are accomplished by adjustment of the length to the diameter ratio of the penetrator, the use of new material such as tungsten and depleted uranium, the use of new propellants, new sabots and new stabilizing fin structures and materials, therefore, and the like. The new propellants require the penetrator to withstand higher temperature in the gun tube since the rod and the guide fins are heated to higher temperatures. Consequently, stabilizing fins which conventionally were made from aluminum alloys are now being made of ferrous alloys which have much higher strength and are capable of withstanding higher temperatures.
When using aluminum alloys, the fins tended to shear readily from the penetrator body when the fins reached the surface of the armor being penetrated and did not produce a substantial retardation force against continued movement of the penetrator rod into their armor. However, higher strength stabilizing fins do not shear until a considerably higher force is applied between the rod body and the fin so that a substantial retardation force is present as the penetrator shaft enters the armor and the fins encounter the armor surface. In other words, a portion of the energy which propels the rod into the armor will be used up by "dragging" the fins through the rod cavity in the armor or in shearing or tearing the fin from the rod. As a result, the full impact energy of the rod is not used in accomplishing its primary objective of passing through a given armor thickness.